Gas turbine

ABSTRACT

In this gas turbine, at a downstream portion of a transition piece of a combustor, inner surfaces of a pair of lateral walls facing each other in a circumferential direction of a turbine rotor form inclination surfaces that incline down to a downstream end of the transition piece in a direction approaching the transition piece of another adjacent combustor that gradually draws closer as it goes to the downstream side of the transition piece in an axis direction.

TECHNICAL FIELD

The present invention relates to a gas turbine including a plurality ofcombustors configured to mix and combust fuel with compressed air togenerate combustion gas, and a turbine having a rotor that is rotated bythe combustion gas from the plurality of combustors, and particularly,to a transition piece of a combustor.

Priority is claimed on Japanese Patent Application No. 2011-203016,filed Sep. 16, 2011, the content of which is incorporated herein byreference.

BACKGROUND ART

Gas turbines include a compressor that brings in the outside air togenerate compressed air, a plurality of combustors that mix and combustfuel with the compressed air to generate combustion gas, and a turbinehaving a rotor that is rotated by the combustion gas from the pluralityof combustors. The plurality of combustors are annularly arranged with arotor as a center. Each combustor has a transition piece through whichcombustion gas is flowed to a gas inlet of the turbine.

If the combustion gas flows out of the transition piece of thecombustor, the combustion gas enters a combustion gas flow channel ofthe turbine from the gas inlet of the turbine. In this case, a Karman'svortex street may be formed in the flow of the combustion gasimmediately after flowing out of the transition piece, an unsteadypressure fluctuation that has this Karman's vortex street as a vibrationsource may resonate at an acoustic eigenvalue, and a large pressurefluctuation may occur, which leads to an operating load.

Thus, in the technique described in the following PTL 1, a largepressure fluctuation is suppressed by limiting a dimension in an axisdirection between a downstream end of a transition piece and an upstreamend of a first stage turbine vane, a dimension in a circumferentialdirection between the upstream end of the first stage turbine vane andthe center between transition pieces that are adjacent to each other inthe circumferential direction centered on a rotor, or the like tospecific ranges.

CITATION LIST Patent Literature

[PTL 1]: Japanese Unexamined Patent Application, First Publication No.2009-197650

SUMMARY OF INVENTION Problem to be Solved by the Invention

The technique described in the above PTL 1 can reliably suppress a largepressure fluctuation at the downstream portion of the transition piece.However, it is desired to further suppress the pressure fluctuation atthe downstream portion of the transition piece and to further enhancethe gas turbine efficiency.

Thus, an object of the invention is to provide a gas turbine that canfurther suppress pressure fluctuation at a downstream portion of atransition piece of a combustor and can further enhance gas turbineefficiency, so as to meet such requests.

Means for Solving the Problem

(1) A gas turbine according to a first aspect of the invention includesa plurality of combustors configured to mix and combust fuel withcompressed air to generate combustion gas; and a turbine having a rotorthat is rotated by the combustion gas from the plurality of combustors.The plurality of combustors are annularly arranged with the rotor as acenter and have a transition piece through which combustion gas isflowed to a gas inlet of the turbine. An inner surface of at least onelateral wall of a pair of lateral walls that constitute a downstreamportion of the transition piece of the combustor and face each other ina circumferential direction of the rotor forms an inclination surfacethat inclines down to a downstream end of the transition piece in adirection approaching the transition piece of another adjacent combustorthat gradually draws closer as it goes to the downstream side of thetransition piece in an axis direction.

Even after the combustion gas that flows toward the downstream sidethrough the inside of the transition piece has flowed out of the insideof the transition piece, the combustion gas tends to flow in a directionalong the inner surfaces of the lateral walls. Therefore, a Karman'svortex street may be formed on the downstream side of a downstream endsurface of the transition piece.

In the gas turbine, the inner surfaces of the lateral walls on thedownstream side of the transition piece form inclination surfaces downto the downstream end of the transition piece. Therefore, flows alongthe inner surfaces of the lateral walls of the transition piece of thecombustor that are adjacent to each other join each other at an angle onthe downstream side of the downstream end surface of the transitionpiece. Therefore, formation of the Karman's vortex street on thedownstream side of the downstream end surface of the transition piececan be suppressed, and the pressure fluctuation of the downstreamportion of the transition piece can be suppressed.

(2) In the gas turbine of the above (1), the turbine may include aplurality of first stage turbine vanes arranged annularly along the gasinlet with the rotor as a center, and each of the first stage turbinevanes may be formed such that a chord direction in which a chord extendsinclines with respect to the circumferential direction. Where a side towhich a downstream end of the first stage turbine vane is located withrespect to an upstream end of the first stage turbine vane in thecircumferential direction is defined as a blade inclination side, atleast one lateral wall of the transition piece may be a lateral wall onthe blade inclination side out of the pair of lateral walls of thetransition piece facing each other in the circumferential direction.

Where the inner surface of only the lateral wall on the bladeinclination side out of the pair of lateral walls of the transitionpiece facing each other in the circumferential direction is theinclination surface, the flow direction of the combustion gas guided bythe inclination surface and the flow direction of the combustion gasguided by the first stage turbine vane are almost the same. As a result,the flow of the combustion gas from the transition piece to the firststage turbine vane becomes smooth. For this reason, even if the innersurface of only the lateral wall on the blade inclination side is theinclination surface, the pressure fluctuation of the downstream portionof the transition piece can be effectively suppressed. In addition, thechord is a line segment that connects the upstream end and downstreamend of a turbine vane.

(3) In the gas turbine of the above (1), both of the inner surfaces ofthe pair of lateral walls of the transition piece facing each other inthe circumferential direction may form the inclination surfaces.

In the gas turbine, formation of the Karman's vortex street on thedownstream side of the respective downstream end surfaces of thetransition piece connected from the inner surfaces of the pair oflateral walls of the transition piece can be suppressed.

(4) In the gas turbine of any one of the above (1) to (3), a ratio A/Bof a dimension A in the axis direction from an upstream end of theinclination surface to a downstream end thereof, to a dimension B in thecircumferential direction from the upstream end of the inclinationsurface to the downstream end thereof, may be 1 to 8.

(5) In the gas turbine according to any one of the above (1) to (4), theinclination surface may include a curved surface, which swells towardthe axis of the transition piece and toward the downstream side, in atleast a portion thereof.

(6) In the gas turbine of any one of the above (1) to (5), the ratio ofthe number of the combustors to the number of the first stage turbinevanes may be an odd number that is equal to or more than 2:3, and aratio S/P of a dimension S in the circumferential direction from anintermediate point between the transition piece of the combustor and thetransition piece of the other combustor to the upstream end of the firststage turbine vane nearest to the intermediate point in thecircumferential direction, to a pitch dimension P of the plurality offirst stage turbine vanes, may be equal to or less than 0.05, between0.2 to 0.55, or between 0.7 to 1.0.

In the gas turbine, any first stage turbine vanes are present relativelyclosely in the circumferential direction, even at the respectivedownstream ends of the transition piece connected from the respectiveinner surfaces of the pair of lateral walls of the transition piece ofany combustor. Therefore, pressure fluctuation on the downstream side ofthe respective transition pieces can be suppressed due to the presenceof the first stage turbine vanes.

(7) In the gas turbine of any one of the above (1) to (6), a ratio L/Pof a dimension L in the axis direction from the downstream end of thetransition piece to the upstream end of the first stage turbine vane, toa pitch dimension P of the plurality of first stage turbine vanes, maybe equal to or less than 0.2.

In the gas turbine, the first stage turbine vane is present relativelyclosely in the axis direction of the transition piece on the downstreamend of the transition piece. Therefore, pressure fluctuation on thedownstream side of the respective transition piece can be suppressed dueto the presence of the first stage turbine vane.

Effects of the Invention

In the invention, formation of the Karman's vortex street on thedownstream side of the downstream end surface of the transition piececan be suppressed, and pressure fluctuation of the downstream portion ofthe transition piece can be suppressed. For this reason, according tothe invention, gas turbine efficiency can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall side view in which main portions of a gas turbinein an embodiment related to the invention are cut out.

FIG. 2 is a cross-sectional view of the circumference of a combustor ofa gas turbine in one embodiment related to the invention.

FIG. 3 is a perspective view of a transition piece in the embodimentrelated to the invention.

FIG. 4 is a cross-sectional view of a downstream side of the transitionpiece in the embodiment related to the invention.

FIG. 5 is a graph showing the relationship between the inclination rateof an inclination surface and pressure fluctuation range in theembodiment related to the invention.

FIG. 6 is an explanatory view showing the positional relationshipbetween the transition piece and first stage turbine vanes in theembodiment related to the invention.

FIG. 7 is an explanatory view showing pressure fluctuations on thedownstream side of the transition piece in the embodiment related to theinvention, FIG. 7( a) shows a case where a circumferential ratio is 10%,FIG. 7( b) shows a case where the circumferential ratio is 22.5%, FIG.7( c) shows a case where the circumferential ratio is 35%, and FIG. 7(d) shows a case where the circumferential ratio is 47.5%.

FIG. 8 is a graph showing the relationship between the pressurefluctuation range and the circumferential ratio on the downstream sideof the transition piece of the embodiment related to the invention.

FIG. 9 is a cross-sectional view on the downstream side of thetransition piece for showing modification examples of an inclinationsurface of the embodiment related to the invention, FIG. 9( a) shows afirst modification example of the inclination surface, and FIG. 9( b)shows a second modification example of the inclination surface.

FIG. 10 is an explanatory view showing the positional relationshipbetween an inclination surface of a transition piece and first stageturbine vanes in a modification example of one embodiment related to theinvention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of a gas turbine related to the inventionwill be described in detail with reference to the drawings.

As shown in FIG. 1, the gas turbine of the present embodiment includes acompressor 1 that compresses the outside air to generate compressed air,a plurality of combustors 10 configured to mix and combust the fuel froma fuel supply source with the compressed air to generate combustion gas,and a turbine 2 that is driven by the combustion gas.

The turbine 2 includes a casing 3, and a turbine rotor 5 that rotateswithin the casing 3. The turbine rotor 5 has a rotor body 6 configuredsuch that a plurality of rotor disks are stacked, and a plurality ofturbine blades 7 that extend in a radial direction from the rotor disksfor each rotor disk. That is, the turbine rotor 5 has a multi-stageturbine blade configuration.

For example, a generator (not shown) that generates electricity by therotation of the turbine rotor 5 is connected to the turbine rotor 5.Additionally, a plurality of turbine vanes 4 that extend in a directionapproaching the rotor body 6 from an inner peripheral surface of thecasing are respectively fixed to the casing 3 on the upstream side ofthe turbine blade 7 of each stage.

The plurality of combustors 10 are fixed to the casing 3 at equalintervals from each other in the circumferential direction with arotation axis Ar of the turbine rotor 5 as a center.

As shown in FIG. 2, the combustor 10 includes a transition piece 20through which high-temperature and high-pressure combustion gas G isflowed from a gas inlet 9 of the turbine 2 into a gas flow passage 8 ofthe turbine 2, and a fuel supply device 11 that supplies fuel andcompressed air Air into the transition piece 20. The turbine blades 7and the turbine vanes 4 of the turbine 2 are arranged in the gas flowpassage 8. The fuel supply device 11 includes a pilot burner 12 thatsupplies pilot fuel X into the transition piece 20 to form a diffusionflame in the transition piece 20, and a plurality of main nozzles 13that premix main fuel Y and the compressed air Air to supply premixedgas into the transition piece 20 and forms a premixed flame in thetransition piece 20.

As shown in FIGS. 2 and 3, the transition piece 20 has a trunk 21 thatforms a tubular shape and has the combustion gas G flowing on an innerperipheral side thereof, and an outlet flange 31 that is provided at adownstream end portion of the trunk 21 and spreads in a direction awayfrom the axis Ac of the transition piece 20.

The cross-sectional shape of the trunk 21 on the downstream side has anoblong shape, and the trunk 21 has, at a downstream portion, a pair oflateral walls 22 facing each other in a circumferential direction Ccentered on the rotation axis Ar of the turbine rotor 5, and a pair oflateral walls 23 facing each other in a radial direction centered on therotation axis Ar.

As shown in FIG. 4, the outlet flange 31 provided at the downstream endportion of the trunk 21 has a flange body portion 32 that spreads in thedirection away from the downstream end of the trunk 21 with respect tothe axis Ac of the transition piece 20, and a facing portion 33 thatextends toward the upstream side from an outer edge of the flange bodyportion 32. A downstream end surface of the flange body portion 32 formsa downstream end surface 20 ea of the transition piece 20. Additionally,a seal member 35 that seals a space between the transition pieces of theadjacent combustors 10 is provided between this facing portion 33 andthe facing portion 33 of the transition piece 20 of an adjacentcombustor 10 in the circumferential direction C. In addition, in thepresent embodiment, the portion of the trunk 21 on the downstream side,that is, the lateral walls 22 and 23 of the downstream portion of thetrunk 21, and the flange body portion 32 are formed from an integrallymolded article.

Respective inner surfaces 24 of the pair of lateral walls 22 facing eachother in the circumferential direction C form inclination surfaces 25that incline down to a downstream end 20 e of the transition piece 20 inthe direction approaching the transition piece 20 of another adjacentcombustor 10 that gradually draws closer as it goes to the downstreamside in the direction of the axis Ac of the transition piece 20. Thatis, the downstream ends of the inclination surfaces 25 are downstreamends 20 e of the transition piece 20.

Even after the combustion gas G that flows toward the downstream sidethrough the inside of the transition piece 20 has flowed out of theinside of the transition piece 20, the combustion gas tends to flow in adirection along the inner surfaces 24 of the lateral walls 22.Therefore, a Karman's vortex street may be formed on the downstream sideof the downstream end surface 20 ea of the flange body portion 32.

In the present embodiment, since the inner surfaces 24 of the lateralwalls 22 of the downstream portion of the transition piece 20 form theinclination surfaces 25, the angle formed by the downstream end surface20 ea of the flange body portion 32 and the inner surfaces 24 of thelateral walls 22 is smaller than that in a case where the inner surfaces24 do not form the inclination surfaces 25. Hence, in the presentembodiment, formation of the Karman's vortex street on the downstreamside of the downstream end surface 20 ea of the flange body portion 32can be suppressed, and pressure fluctuation of the downstream portion ofthe transition piece 20 can be suppressed.

Here, since the pressure fluctuation range of the downstream portion ofthe transition piece 20 when changing the inclination rate of eachinclination surface 25 was simulated, the results of this simulationwill be described. In addition, in this simulation, as shown in FIG. 4,the ratio A/B of a dimension A in the direction of the axis Ac from theupstream end 25 s to the downstream end 20 e, to a dimension B in thecircumferential direction C from an upstream end 25 s of the inclinationsurface 25 to a downstream end 20 e (=the downstream end of thetransition piece 20) thereof, is defined as the inclination rate of theinclination surface 25.

As a result of this simulation, as shown in FIG. 5, it can be understoodthat, when the inclination rate A/B is 1 to 8, a pressure fluctuationrange ΔP of the downstream portion of the combustor 10 is small. This isbecause, where the inclination rate A/B is less than 1 and more than 8,the inclination is too steep or too gentle and therefore, the effect asthe inclination surface 25 cannot be sufficiently obtained. Moreover, itcan also be understood that, if the inclination rate A/B of theinclination surface 25 is 2 to 6, the pressure fluctuation range ΔP isextremely small. In addition, as the flow velocity of the combustion gasG that flows through the inside of the transition piece 20 becomeshigher, the pressure fluctuation range ΔP also becomes larger. However,the relationship between the inclination rate A/B of the inclinationsurface 25 and the pressure fluctuation range ΔP is fundamentally thesame even if the flow velocity of the combustion gas G that flowsthrough the inside of the transition piece 20 changes.

For this reason, it can be said that the preferable range Ra of theinclination rate A/B of the inclination surface 25 is 1 to 8, and themore preferable range Rb is 2 to 6.

Moreover, here, since the pressure fluctuation range at the downstreamportion of the combustor 10 when changing the relative positions betweenthe transition piece 20 and the first stage turbine vanes 4 a was alsosimulated herein, the results of this simulation will also be described.Specifically, as shown in FIG. 6, the relationship between the pressurefluctuation range ΔP, and the ratio S/P (hereinafter referred to as acircumferential ratio S/P) of a dimension S in the circumferentialdirection C from an intermediate point M between the transition piece 20of a specific combustor 10 a and the transition piece 20 of anotheradjacent combustor 10 b adjacent to the specific combustor on one sidein the circumferential direction C to an upstream end 4 s of the firststage turbine vane 4 a nearest to the intermediate point on one side inthe circumferential direction C, to a pitch dimension P in thecircumferential direction C of the plurality of first stage turbinevanes 4 a, was simulated.

In addition, this simulation was performed with the ratio of the numberNc of the combustors 10 and the number Ns of the first stage turbinevanes 4 a being 2:3 and with the inclination rate A/B of the inclinationsurface 25 of the transition piece 20 being 2.75. Moreover, thissimulation was performed with the ratio L/P (hereinafter referred to asan axis-direction ratio L/P) of a dimension L in the direction of theaxis Ac from the downstream end 20 e of the transition piece 20 to theupstream end 4 s of the first stage turbine vane 4 a to the pitchdimension P being 12%.

As shown in FIG. 8, where the axis-direction ratio L/P is 12%, there isalmost no unsteady pressure fluctuation with the circumferential ratioS/P being 0% to 5%. However, where the circumferential ratio S/P exceeds5%, a large pressure fluctuation range ΔP begins to be seen, and wherethe circumferential ratio S/P reaches 10%, the pressure fluctuationrange ΔP becomes larger.

As shown in FIG. 7( a), where the circumferential ratio S/P is 10%, anunsteady pressure fluctuation is not seen on the downstream side betweenthe transition piece 20 of a specific combustor 10 a and the transitionpiece 20 of another combustor 10 b that is adjacent to the specificcombustor on one side in the circumferential direction C. However, onthe downstream side between the transition piece 20 of the specificcombustor 10 a and the transition piece 20 of another combustor 10 cthat is adjacent to the specific combustor on the other side in thecircumferential direction C, the Karman's vortex street V is generatedand a relatively large unsteady pressure fluctuation occurs. It isconsidered that this is because the dimension in the circumferentialdirection C from a position between the transition piece 20 of thespecific combustor 10 a and the transition piece 20 of the othercombustor 10 c that is adjacent to the specific combustor on the otherside in the circumferential direction C to the upstream end 4 s of thefirst stage turbine vane 4 a nearest to the position in thecircumferential direction C becomes large. In addition, thin lines inFIG. 7 indicate isostatic lines.

Hence, it is be considered that, where the circumferential ratio S/Preaches 10%, the pressure fluctuation range ΔP becomes large. However,in this simulation, since the inclination rate A/B of the inclinationsurface 25 is 2.75 that is in a more preferable range Rb (2 to 6), thepressure fluctuation range ΔP is smaller than that in a case where theinclination surface 25 is not formed, or the like.

The pressure fluctuation range ΔP becomes drastically small as shown inFIG. 8 if the circumferential ratio S/P reaches 20%, and an unsteadypressure fluctuation is hardly seen where the circumferential ratio S/Preaches 22.5%. As shown in FIG. 7( b), where the circumferential ratioS/P is 22.5%, an unsteady pressure fluctuation is hardly seen on thedownstream side between the transition piece 20 of the specificcombustor 10 a and the transition piece 20 of the other combustor 10 bthat is adjacent to the specific combustor on one side in thecircumferential direction C and even on the downstream side between thetransition piece 20 of the specific combustor 10 a and the transitionpiece 20 of the other combustor 10 c that is adjacent to the specificcombustor on the other side in the circumferential direction C.

The unsteady pressure fluctuation, as shown in FIG. 7( c) and FIG. 7(d), are hardly seen even where the circumferential ratios S/P are 35 and47.5%. However, as shown in FIG. 8, where the circumferential ratio S/Pexceeds 55%, a large pressure fluctuation range ΔP begins to be seenagain, and where the circumferential ratio S/P reaches 60%, the pressurefluctuation range ΔP becomes larger. It is considered that this isbecause the dimension in the circumferential direction C from theposition between the transition piece 20 of the specific combustor 10 aand the transition piece 20 of the other combustor 10 b that is adjacentto the specific combustor on one side in the circumferential direction Cto the upstream end 4 s of the first stage turbine vane 4 a nearest tothe position in the circumferential direction C is large. That is, it isconsidered that, where circumferential ratio S/P is 60%, the samephenomenon occurs for the reason that is fundamentally the same as thatwhere the circumferential ratio S/P is 10%.

The pressure fluctuation range ΔP becomes drastically small where thecircumferential ratio S/P reaches 70%, and an unsteady pressurefluctuation is hardly seen where the circumferential ratio S/P becomes72.5%. An unsteady pressure fluctuation is hardly seen thereafter untilthe circumferential ratio S/P reaches 100%.

As described above, it can be understood that, when where thecircumferential ratios S/P are 0 to 5%, 20 to 55%, and 70 to 100%, anunsteady pressure fluctuation is hardly seen, and the pressurefluctuation range ΔP of the downstream portion of the transition piece20 becomes extremely small. That is, it can be understood that thepreferable ranges Rc of the circumferential ratio S/P are 0 to 5%, 20 to55%, and 70 to 100%.

Moreover, here, the axis-direction ratio L/P was changed and therelationship between the circumferential ratio S/P and the pressurefluctuation range ΔP was simulated similarly to the above.

As shown in FIG. 8, even where the axis-direction ratios L/P are 18%,20%, and 27%, the same tendency as that where the aforementionedaxis-direction ratio L/P is 12% is seen as the changes in the pressurefluctuation range ΔP to the changes in the circumferential ratio S/P.That is, it can be understood that, when the circumferential ratios S/Pare 0 to 5%, 20 to 55%, and 70 to 100% similar to a case where theaforementioned axis-direction ratio L/P is 12%, the pressure fluctuationrange ΔP of the downstream portion of the combustor 10 is relativelysmall compared to cases where the circumferential ratios S/P are 5 to20% and 55 to 70%.

However, it can be understood that, in cases where the circumferentialratios S/P are 0 to 5%, 20 to 55%, and 70 to 100% where theaxis-direction ratios L/P are 18% and 20%, an unsteady pressurefluctuation is hardly seen and the absolute value of the pressurefluctuation range ΔP is small similar to when the aforementionedaxis-direction ratio UP is 12%, but even in cases where thecircumferential ratios S/P are 0 to 5%, 20 to 55%, and 70 to 100% wherethe axis-direction ratio L/P is 27%, the absolute value of the pressurefluctuation range ΔP is large.

That is, it can be understood that the pressure fluctuation range ΔPbecomes small as the axis-direction ratio L/P is made equal to or lessthan 20%.

Additionally, the above-described simulation results are results in acase where the ratio of the number Nc of the combustor 10 and the numberNs of the first stage turbine vanes 4 a is 2:3. However, it isconsidered that, even in the cases of Nc:Ns=2:5, Nc:Ns=2:7, andNc:Ns=2:9 or more, the same results as in the above are obtainedregarding the relationship between the relative positions of thetransition piece 20 and the first stage turbine vanes 4 a and thepressure fluctuation range ΔP on the downstream portion of thetransition piece 20. However, as the number Ns of the first stageturbine vanes 4 a becomes larger than the number Nc of the combustors10, the absolute value of the pressure fluctuation range ΔP when thepressure fluctuation range ΔP becomes large becomes smaller at any valueof the circumferential ratio S/P or the axis-direction ratio L/P. As aresult, it is considered that, where the number Ns of the first stageturbine vanes 4 a becomes larger, an unsteady pressure fluctuation ishardly seen at any value of the circumferential ratio S/P or theaxis-direction ratio L/P.

In addition, where the number Nc of the combustors 10 and the number Nsof the first stage turbine vanes 4 a is 1:natural number, the upstreamend 4 s of the first stage turbine vane 4 a can be arranged directlybelow the position between the transition piece 20 of each combustor 10and the other transition piece 20 that is adjacent to the combustor ofeach combustor. Therefore, an unsteady pressure fluctuation can bealmost eliminated by arranging the first stage turbine vanes 4 a in thisway.

Next, various modification examples of the inclination surface 25 of thetransition piece 20 will be described.

In the inclination surface 25 of the above embodiment, the whole surfacefrom the upstream end 25 s of the inclination surface to the downstreamend 20 e thereof is a planar surface. However, the inclination surface25 does not need to be a planar surface as a whole, and may also includecurved surfaces in at least portions thereof.

Specifically, the curved surfaces, as shown in FIG. 9, are curvedsurfaces 26 a, 26 b, and 26 c that swell smoothly toward the axis Ac ofthe transition piece 20 and toward the downstream side. For example, asfor the curved surface 26 a, as shown in FIG. 9 a, in a boundary region26 a between the inclination surface 25 and the downstream end surface20 ea of the flange body portion 32, that is, a downstream end of thecurved surface 26 a coincides with the downstream end 20 e of theinclination surface 25. Additionally, as for the curved surface 26 b, anupstream end of the curved surface 26 b coincides with the upstream end25 s of the inclination surface 25. Additionally, as shown in FIG. 9(b), the whole inclination surface 25 is the curved surface 26 c.

If the curved surfaces are adopted in at least a portion of theinclination surface 25 in this way, a place where the flow direction ofthe combustion gas G changes drastically is eliminated. Therefore,formation of the Karman's vortex street on the downstream side of thedownstream end surface 20 ea of the transition piece 20 can be furthersuppressed, and the pressure fluctuation of the downstream portion ofthe transition piece 20 can be more effectively suppressed. For thisreason, when the curved surfaces are adopted in at least a portion ofthe inclination surface 25, the preferable range Ra of the inclinationrate A/B of the inclination surface 25 becomes wider than the range of 1to 8 that is described above.

Additionally, in the above embodiment, the respective inner surfaces 24of the pair of lateral walls 22 facing each other in the circumferentialdirection C form the inclination surfaces 25. However, even if only oneinner surface 24 forms the inclination surface 25, the pressurefluctuation of the downstream portion of the transition piece 20 can besuppressed. In this case, as shown in FIG. 10, where the side to whichthe downstream end 4 e of a first stage turbine vane 4 a is located withrespect to the upstream end 4 s of the first stage turbine vane 4 a inthe circumferential direction C is defined as a blade inclination sideCa, it is preferable that the inner surface 24 of the lateral wall 22(22 b in the case of FIG. 10) on the blade inclination side Ca out ofthe pair of lateral walls 22 (22 a and 22 b in the case of FIG. 10)facing each other in the circumferential direction C forms theinclination surface 25. This is because the flow direction of thecombustion gas G guided by the inclination surface 25, and the directionof a chord that is a line segment that connects the upstream end 4 s andthe downstream end 4 e of the first stage turbine vane 4 a, that is, theflow direction of the combustion gas G guided by the first stage turbinevane 4 a, are almost the same, and consequently, the flow of thecombustion gas G from the transition piece 20 to the first stage turbinevane 4 a becomes smooth and the pressure fluctuation of the downstreamportion of the transition piece 20 can be effectively suppressed.

In addition, as described above, even if only the inner surface 24 ofany one lateral wall 22 (22 a or 22 b in the case of FIG. 10) out of thepair of lateral walls 22 facing each other in the circumferentialdirection C forms the inclination surface 25, the relationship betweenthe relative positions of the transition piece 20 and the first stageturbine vanes 4 a and the pressure fluctuation range ΔP at thedownstream portion of the transition piece 20 is fundamentally the sameas in the above simulation results.

REFERENCE SIGNS LIST

1: COMPRESSOR

2: TURBINE

3: CASING

4: TURBINE VANE

4 a: FIRST STAGE TURBINE VANE

4 s: UPSTREAM END (OF TURBINE VANE)

4 e: DOWNSTREAM END (OF TURBINE VANE)

5: TURBINE ROTOR

6: ROTOR BODY

7: TURBINE BLADE

8: GAS FLOW PASSAGE

9: GAS INLET

10: COMBUSTOR

20: TRANSITION PIECE

20 e: DOWNSTREAM END (OF TRANSITION PIECE OR INCLINATION SURFACE)

20 ea: DOWNSTREAM END SURFACE (OF TRANSITION PIECE OR FLANGE BODYPORTION)

21: TRUNK

22, 22 a, 22 b, 23: LATERAL WALL

24: INNER SURFACE

25: INCLINATION SURFACE

25 s: UPSTREAM END (OF INCLINATION SURFACE)

26 a, 26 b, 26 c: CURVED SURFACE

1. A gas turbine comprising: a plurality of combustors configured to mixand combust fuel with compressed air to generate combustion gas; and aturbine having a rotor that is rotated by the combustion gas from theplurality of combustors, wherein the plurality of combustors areannularly arranged with the rotor as a center and have a transitionpiece through which combustion gas is flowed to a gas inlet of theturbine, and wherein, at a downstream portion of the transition piece ofthe combustor, an inner surface of at least one lateral wall out of apair of lateral walls facing each other in a circumferential directionof the rotor forms an inclination surface that inclines down to adownstream end of the transition piece in a direction approaching thetransition piece of another adjacent combustor that gradually drawscloser as it goes to the downstream side of the transition piece in anaxis direction.
 2. The gas turbine according to claim 1, wherein theturbine includes a plurality of first stage turbine vanes arrangedannularly along the gas inlet with the rotor as a center, and each ofthe first stage turbine vanes are formed such that a chord direction inwhich a chord extends inclines with respect to the circumferentialdirection, and wherein where the side to which a downstream end of thefirst stage turbine vane is located with respect to an upstream end ofthe first stage turbine vane in the circumferential direction is definedas a blade inclination side, at least one lateral wall of the transitionpiece is a lateral wall on the blade inclination side out of the pair oflateral walls of the transition piece facing each other in thecircumferential direction.
 3. The a gas turbine according to claim 1,wherein both of the inner surfaces of the pair of lateral walls of thetransition piece facing each other in the circumferential direction formthe inclination surfaces.
 4. The gas turbine according to claim 1,wherein a ratio A/B of a dimension A in the axis direction from anupstream end of the inclination surface to a downstream end thereof, toa dimension B in the circumferential direction from the upstream end ofthe inclination surface to the downstream end thereof, is 1 to
 8. 5. Thegas turbine according to claim 1, wherein the inclination surfaceincludes a curved surface, which swells toward the axis of thetransition piece and toward the downstream side, in at least a portionthereof.
 6. The gas turbine according to claim 1, wherein the ratio ofthe number of the combustors and the number of the first stage turbinevanes is an odd number that is equal to or more than 2:3, and wherein aratio S/P of a dimension S in the circumferential direction from anintermediate point between the transition piece of the combustor and thetransition piece of the other combustor to the upstream end of the firststage turbine vane nearest to the intermediate point in thecircumferential direction, to a pitch dimension P of the plurality offirst stage turbine vanes, is equal to or less than 0.05, between 0.2 to0.55, or between 0.7 to 1.0.
 7. The gas turbine according to claim 1,wherein a ratio L/P of a dimension L in the axis direction from thedownstream end of the transition piece to the upstream end of the firststage turbine vane, to a pitch dimension P of the plurality of firststage turbine vanes, is equal to or less than 0.2.
 8. A combustorarranged so as to be adjacent to another one in a circumferentialdirection centered around a rotation axis of a rotor constituting aturbine and configured to generate combustion gas which rotates therotor, the combustor comprising: a transition piece having a pair oflateral walls facing each other in a circumferential direction centeredaround the rotation axis and through which combustion gas is flowed to agas inlet of the turbine, wherein an inner surface of at least onelateral wall out of the pair of lateral walls facing each other in thecircumferential direction forms an inclination surface that inclinesdown to a downstream end of the transition piece in a directionapproaching the transition piece of another adjacent combustor thatgradually draws closer as it goes to the downstream side of thetransition piece in an axis direction.
 9. The combustor according toclaim 8, wherein both of the inner surfaces of the pair of lateral wallsof the transition piece facing each other in the circumferentialdirection form the inclination surfaces.
 10. The combustor according toclaim 8, wherein a ratio A/B of a dimension A in the axis direction froman upstream end of the inclination surface to a downstream end thereof,to a dimension B in the circumferential direction from the upstream endof the inclination surface to the downstream end thereof, is 1 to
 8. 11.The combustor according to claim 8, wherein the inclination surfaceincludes a curved surface, which swells toward the axis of thetransition piece and toward the downstream side, in at least a portionthereof.